Why doesn't the snow and ice on the mountain melt all the year round?

The reason why the snow and ice on the mountain don't melt all the year round is that the weather on the mountain is much colder than the plain in the same area. The higher the mountain, the thinner the air, and the easier it is to lose heat from the sun. About every increase of 100 m, the temperature will drop by about 0.6℃. So at a certain height, the temperature will drop below 0℃, and the ice and snow at this height will not melt all year round. The dividing line of this height is called the snow line. The closer to the poles, the lower the snow line position; The closer to the equator, the higher the position of the snow line. After the top of the mountain is covered with snow and ice, 50% ~ 90% of the light and heat will be reflected back due to the strong reflection of the snow and ice surface, which makes the temperature here low and the snow and ice are not easy to melt. So at the top of the mountain above the snow line, there will be snow all year round. Of course, there must be snow here, and there must be a place to pile snow on the top of the mountain. Therefore, not all mountains can pile up ice and snow. If there is strong sunlight, there will be some melting, but soon there will be snowfall to make up for it, so ice and snow can always exist and form glaciers to move down.